1. Field of the Invention
The present invention broadly relates to vehicle brake systems. More specifically, the present invention relates to eliminating undesirable brake fluid pressure within brake conduits that builds up during brake application in anti-locking brake systems. The present invention encompasses a method of controlling the normally closed outlet valves within an anti-locking brake system to release unwanted pressure by allowing the hydraulic brake fluid to return to the system's reservoir and, thereby, reestablish the pressure within the system at reservoir pressure.
2. The Prior Art.
Modern automobile anti-locking brake systems facilitate maintaining vehicle stability during brake application. Brake systems essentially work by controlling the pressure of the hydraulic brake fluid within the brake conduits that make up the anti-locking brake system. Anti-locking brake systems inherently include a pressure buildup within the conduits between the master cylinder and the brake pads. Heat builds up within the brake system when the brakes are applied. Increased heat causes pressure buildup within the system because there is a fixed volume of fluid. This increased pressure buildup is undesirable because it causes brake drag after the brake pedal is released by the user. The excess pressure must be released within the system in order to avoid brake drag. Brake drag is a progressive problem; it, in turn, causes additional heat buildup and further brake drag. Several methods attempt to avoid this excessive pressure and brake drag; however these methods have several shortcomings and drawbacks.
One attempt at avoiding excess pressure buildup and resulting brake drag in a hydraulic anti-locking brake system includes using a compensation port design in the master cylinder. The compensation port design has limited use for anti-locking brake systems because the brake fluid is returned to the master cylinder under high pressure. The compensation port design includes a lip seal that is typically fashioned of rubber. The lip seal is connected to the piston within the master cylinder that activates the brakes. The inherent high pressure within an anti-locking brake system forces brake fluid against the lip seal, causing the lip seal to extrude into the compensation port. Any further movement of the brake pedal tears the lip seal because it extrudes into the compensation port. This results in a damaged lip seal, and therefore, an inadequate brake system.
Another attempt at relieving the unwanted pressure buildup within an anti-locking brake system includes central valves connected to the master cylinder. The central valve design typically includes at least one ball and seat valve connected between the master cylinder and the brake fluid reservoir. When the brakes are applied, the central valve remains closed so the brake fluid will be forced into the brake conduits causing a braking action to slow down the vehicle. Once the brake pedal is released, the remaining excess pressure within the brake conduits must be released to avoid brake drag. The central valves facilitate releasing the excess, unwanted pressure by opening the compensation port and, thereby, allowing the fluid to flow back through the master cylinder into the brake fluid reservoir. The central valve compensation design avoids the problems involved with the lip seal/compensation port design. However, the central valve design includes several drawbacks.
First, the central valve design is extremely complicated. Second, the central valve design is very difficult to assemble because of the number of parts involved and the nature of those parts. Therefore, the central valve design is both complicated and difficult to assemble, it adds cost to the braking system, in turn adding cost to the vehicle. Further, central valves, when opened as just described, must be reclosed upon a subsequent brake application. The time it takes to reclose the central valves introduces lost travel time and a consequent delay in proper function within the brake system.